This invention relates generally to audio enhancement systems and methods for improving the realism and dramatic effects obtainable from stereo sound reproduction. More particularly, this invention relates to apparatus and methods for enhancing sound generated in a surround sound environment having separate front and rear audio channels.
The advent of stereo surround-sound audio systems, i.e., audio systems having separate audio channels for front and rear speakers, has brought a more realistic and enveloping audio experience to listeners. Such systems, such as Dolby Laboratories Pro-Logic system, may use a matrixing scheme to store four or more separate audio channels on just two audio recording tracks. Upon dematrixing, the Pro-Logic audio system delivers distinct audio signals to a left-front speaker, a right-front speaker, a center speaker, and to surround speakers placed behind a listener.
More recently, surround sound systems have emerged which can deliver completely separate forward and rear audio channels. One such system is Dolby Laboratories five-channel digital system dubbed "AC-3." An audio component which has Dolby AC-3 capability can deliver five discrete channels to speakers placed around a listening environment (left-front, center, right-front, left-surround, and right-surround). Unlike previous surround-sound systems, all five of the distinct channels of the Dolby AC-3 system have full bandwidth capability. This allows for more dynamic and volume range of the rear, or "surround", channels.
The discrete full-bandwidth channels of the Dolby AC-3 system have been touted as increasing localization of stereo sound effects within a sound field. This localization results from the distinct audio channels which feed a separate speaker within the surround sound environment. As a result, sound information can be channeled to any speaker within the system. Moreover, because the AC-3 audio channels are not limited in audio bandwidth, all of the channels can be used for both ambient and direct sound effects.
Although localization of sounds to some extent is beneficial and may greatly increase realism upon audio playback, the capabilities of systems such as Dolby AC-3 and Pro-Logic are limited. For example, a sound field which surrounds a listener can be created by directing sounds to five separate speakers placed around the listener. However, the surround-sound field may be perceived by the listener as containing five discrete point sources from which sounds emanate. In certain surround-sound audio systems, sounds which are intended to move from one rear speaker to another rear speaker may seem, from a listener's perspective, to leap across the rear sound stage. Similarly, sounds which are intended to move from a forward-left speaker to a rear-left speaker may likewise appear to leap across the left sound stage.
Despite the advances in audio reproduction systems, and particularly those having surround sound capability, there is a need for an audio enhancement system which can improve upon the realism of these audio reproduction systems. The audio enhancement system disclosed herein fulfills this need.